Inventories (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 13,740	$ 8,231
Supplies and service parts	23,701	21,841
Finished products	40,389	36,690
Inventory at FIFO cost	77,830	66,762
Excess of FIFO cost over LIFO cost	(4,483)	(4,483)
Total inventory, net	$ 73,347	$ 62,279